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110 Cards in this Set
- Front
- Back
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1. What does it mean that bacteria are haploid?
What are eukaryotes? |
The heritable unit is a single copy of the genetic material
Diploid so the heritable unit is two copies of the genetic material |
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2. What is a mutation?
How is a mutation first detected? How does mutation detection compare between diploids and haploids? |
Change in the nucleotide sequence of a gene
First detected by changes in observable characteristics (phenotype) **this is controlled by the genotype Diploids -not east to detect mutations -mutations are often recessive Haploids -mutant isolation is much easier |
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3. What is the mutation rate?
What is the spontaneous mutation rate? |
Probability that a cell will mutate in a particular gene during a generation
1 x 10^6 |
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4. How are mutations and mutation rates important clinically regarding the use of antibiotics?
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Use of antibiotics creates a situation of absolute selection
For example a rifampicin-resistant mutant can rapidly constitute 100% of the population when the antibiotic is used to treat a patient |
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5. What happens if the mutation occurs during antibiotic treatment?
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It does not get established b/c the mutated organism remains sensitive to the antibiotic for some time (phenotypic lag)
**UNLESS the antibiotic treatment is interrupted **Mutation is not cause by antibiotic though |
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6. What is rifampicin resistance?
What patients is this especially important to? What antibiotic course must be used for these patients? Why? |
Mutation in gene ropB coding for beta subunit of RNA polymerase
Patients with TB Combined antibiotic therpay (rifampicin plus isoniazid) Chance of simultaneoulsy obtaining resistance to both antibiotics is 1 in 10^14 |
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7. What is phenotypic lag?
How is this seen in rifampicin resistant bacteria? |
Delay in phenotypic expression of the genotypic change (the mutation)
**lag till mutation (change in DNA) is expressed It is only after many generations that the sensitive subunits are diluted out and the bacteria become resistant to rifampicin |
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8. What three mutations that DNA can undergo?
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1. Base substitution
2. Frameshift mutation 3. Large deletion |
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9. What are the two types of base substitution mutations?
In general what two things can base substitutions cause? |
1. Transitions
-purine to purine -pyrimidine to pyrimidine 2. Transversions -purine to pyrimidine -pyrimidine to purine Can cause either... 1. Mis-sense mutation - different AA 2. Non-sense mutation - stop codon |
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10. What is a mis-sense mutation?
What is a non-sense mutation? |
Triplet is changed specifying a different amino acid and causing loss of protein functions
A translation stop codon is added |
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11. Why does a frame shift mutation occur?
Does deletion or insertion of three bases cause a frame shift mutation? |
Insertion or deletion of a nucleotide
**either one or two bases causes a frame shift mutation NO |
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12. What does a deletion mutation result in?
What type of mutation are point mutations? Are point mutations reversible? |
Loss of a large section of DNA which includes the loss of several genes
Base substitutions Are reversible so back mutations occur |
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13. What are some mutagens that cause mutations?
Five examples |
1. Base analog
2. Intercalating agent 3. UV irradiation 4. Chemicals that react w/ DNA 5. X-rays |
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14. What are base analogs?
What does 2-AP substitute for? What about 5-BU? How are these substitutions? |
Chemicals that look like normal bases (2-AP or 5-BU) that can substitute for normal bases in DNA
2-AP subs for adenine 5-BU subs for thymine They do no base-pair as accurately as the natural bases and occasionally pair w/ the wrong base |
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15. What type of mutation do base analogs cause?
What base pairing occurs when there is a mutation? |
Cause a point mutation
**Transition mutation 2-AP pairs w/ cytosine 5-BU pairs w/ guanine |
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16. What are intercalating agents?
What type of mutation do they cause? When do these mutations occur? |
Proflavine dyes that insert themselves (intercalate) between successive base pairs in the DNA double helix
Frame shift mutations During DNA replication |
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17. What type of mutation does UV light cause?
How do x-rays affect DNA? |
Pyrimidine dimer formation
Affect through oxidation resulting from production of intracellular H2O2 and/or free radicals **formation of free radicals such as superoxide and hydroxyl |
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18. What is a temperature sensitive (TS) mutation?
A TS mutation is an example of what type of mutation? Why? |
Production of a completely or partially non-functional protein at an elevated temperature
Conditional lethal mutation B/c it's lethal under one set of conditions but not lethal under another set |
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19. What is a suppressor mutation?
What are the two types of suppressor mutation? |
When a 2nd mutations suppresses the effects of the first mutation
**corrects or compensates for errors in the product of a mutated gene 1. Intragenic suppressor (in the same gene) 2. Extragenic suppressor (intergenic) |
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20. What is an example of an intragenic suppressor?
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Insertion of a base reverses a frame shift mutation cause by a previous deletion
Intragenic suppressor mutation is the second mutation It suppresses the phenotypic effect of the first mutation |
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21. What is an extragenic suppressor?
What is the best known extragenic suppressor? |
A second mutation in a different gene corrects the effect of a previous mutation
Non-sense suppressor |
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22. How does an extragenic suppressor mutation suppress a non-sense mutation?
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A mutant tRNA (extragenic suppressor) can read a nonsense mutation
An AA is still inserted into the growing polypeptide chain and elongation is not terminated **non-sense suppressor If the AA substitute is not critical to protein than complete or partial function of protein is restored |
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23. What does the Ames test look for?
If a chemical is found to be a mutagen by the Ames test then what is it assumed to be? If colonies grow around the spot on the Ames test then what does that mean? Why is it a mutagen? |
Tests for mutagenicity
A carcinogen Suspect compound is indeed a mutagen (potentially a carcinogen) It caused an increased frequency of back mutations or reversions from auxotrophy to prototrophy |
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24. What is a prototrophy?
What is an auxotroph? What does the Ames test use? |
Nutritionally independent strain that only requires minimal nutrients
Nutritionally dependent strain that requires additional nutrients Uses auxotrophs of Salmonella typhimurium |
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25. Why can the genetic change in bacteria occur much faster than the mutation rate?
What three things can cause genetic changes in bacteria? What are all three mediate by? |
Due to the transfer of genes between bacterial populations
1. Transformation 2. Transduction 3. Conjugation Mediated by homologous recombination |
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26. What does homologous recombination require?
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1. Reasonably long regions of similarity or identity between the donor and recipient DNA
2. RecA protein |
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27. What is transformation?
Is polarity necessary for transformation? What enzyme does transfer of DNA by the process of transformation require? |
Process in which free, soluble, naked DNA extracted from or spontaneously released by one bacterium (donor) gets into another (recipient)
Need be no polarity **recipient can also act as donor and vice verse DNAse susceptible |
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28. What is competence?
When does competence generally occur? In some species what is competence due to? |
State of a cell that allows it to take up DNA
Occurs only in certain growth conditions Protein competence factor on surface of recipient |
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29. How was transformation first discovered?
What was this transformation called? What were experiments with the type transformation phenomenon the first to show? |
Transformed an avirulent, non-encapsulated mutant of S. pneumoniae to a virulent, capsulated strain
Type transformation First to show that DNA is hereditary material |
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30. How are encapsulated bacterial colonies?
How are non-encapsulated bacterial colonies? |
Have a smooth appearance
**S1, S2, S3, etc. Have a rough appearance **R1, R2, R3, etc. |
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31. In gram-positive bacteria such as S. pneumonia, S. mutans, and S. sangus how does transformation occur?
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Only a single strand of DNA enters the recipient and recombines by homologous recombination w/ the chromosome of the recipient
Other strange is digested at the surface |
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32. In gram-negative bacteria such as A.A. how does transformation occur?
Three steps... |
1. Double stranded DNA enters recipient
2. Surface determinants recognize signature sequence on DNA **DNA from almost all other species is excluded 3. Single strand is incorporated into recipient chromosome |
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33. In S. pneumonia how is S1 (encapsulated)?
How is killed S1? How is R1 (non-encapsulated)? In S. pneumoniae how does transformation occur between S1 and R1? |
Pathogen
Non-pathogen Non-pathogen Combine live R1 with killed S1 then S1 is recovered and it becomes pathogenic again |
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34. What is transduction preformed by?
How does this occur? Six steps... |
Bacteriophage
**bacterial viruses 1. Phage attaches to surface receptors 2. Phage injects nucleic acid 3. Host cell copies and expresses nucleic acid 4. Host synthesizes phage heads, tails and nucleic acids 5. Nucleic acids are packaged in heads and tails are added 6. Host bacteria lyse releasing mature phage particles |
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35. How are bacteriophages assayed?
Where are plaques? |
By their ability to for plaques (holes) on lawns of bacteria
Where phage has infected bacterium, made copies and burst out infect adjacent bacteria |
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36. What is transduction?
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Process in which "donor" bacterial DNA in incorporated (by mistake) into a phage head when phage particles are being assembled (replicated)
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37. What happens in generalized transduction?
Does the phage particle carry any phage DNA? Can the phage form plaques? What is the phage often called? |
Any fragment of "donor" chromosome can be packaged into the phage head
Phage particle carries no phage DNA Cannot form plaques Often called a transducing particle **can transfer bacterial DNA to a "recipient" |
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38. What are the main requirements for transduction?
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1. Suitable phage
2. Availability of a specific phage receptor on the surface of the bacteria |
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39. What is site-specific recombination?
Does it require RecA protein? What is lysogeny? |
Bacteriophages that are able to insert their DNA into the bacterial chromosome at a particular site
No Phenomenon where phage DNA is maintained in a quiescent state as part of the bacterial chromosome as the bacteria grow and divide **only one or two phage genes are expressed in this lysogenic (prophage) state |
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40. What are the steps in the induction of phage DNA by an external signal?
Four steps.... |
1. Phage DNA is excised from lysogenic bacteria
2. Phage goes into lytic path 3. Form infective phages 4. Lyse of host bacteria |
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41. What type of plaques do lytic phages give?
What type of plaques do lysogenic phages give? |
Clear plaques
Turbid plaques |
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42. What type of DNA do specialized transducing particles contain?
Can specialized transducing particles form plaques? |
Contain phage DNA that is covalently joined to the bacterial DNA
May be able to form plaques |
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43. What does conjugation involved?
What does conjugation between strains of E. coli K12 depend on? |
Involves "sexual" polarity so there is a distinct donor and recipient strains w/in a species
The F (fertility) Factor |
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44. What is the F factor?
How is the DNA in the F factor? What is the F plasmid? |
F factor is a plasmid
Double stranded, circular DNA F plasmid is its own replicon **replicates separately from the chromosome |
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45. What is the pilus made of?
What is the pilus necessary for? What does the pilus act as? |
Made of protein subunits
Necessary for conjugation Acts as a grappling hook for cell-to-cell contact which results in DNA transfer |
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46. How does contact occur during conjugation?
What distinguishes conjugation from transformation and transduction? What is production of the donor pilus and transfer of DNA to the recipient due to? |
Contact via pilus followed by closer, intimate contact
Requirement for cell-to-cell contact Due to the presence in the donor of the sex factor labeled F factor |
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47. What are the steps in bacterial conjugation resulting in the introduction of an F plasmid into an F- cell by replicative transfer from an F+ cell?
Three steps... What happens to the sex factor (F)? |
1. Pilus makes contact w/ recipient
2. Trigger F replication 3. Transfer of one DNA strand of F to the recipient where that strand is replicated Entire sex factor goes over to the recipient making it a donor |
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48. In a mixture of donors and recipients how is the transfer of the sex factor?
What is an infectious or epidemic transfer of the F plasmid? Why is conjugation important amongst the Enterobacteriaceae? Why can F integrate into about 25 different sites of the chromosome? Of the three methods for transferring DNA which often result in the transfer of more DNA (genes)? |
Transfer is rapid and widespread
Entire population becomes F+ It is the main method for the spread of antibiotic resistance B/c it the chromosome have short homologous sequences Conjugation |
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49. What do the three types of F mediated conjugation depend upon?
What are they? |
Depend on which of the three interchangeable forms of the F factor is present in the donor
1. F+ strains --> infectious 2. F' strains --> infectious 3. Hfr strains --> not infectious |
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50. What is F'?
As in the F+ mating what happens to the recipient upon receipt of F'? What type of transfer is F'? |
The F factor w/ added chromosomal genes
The recipient becomes the donor Epidemic transfer **entire population becomes F' |
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51. What happens in Hfr x F mating?
What happens to the transfer though in this mating? What happens to the recipient at the end of transfer? What does Hfr stand for? |
The F factor is incorporated into the chromosome in Hfr strains becoming part of the chromosome replicon
It spontaneously stops and at most 1/3 of the chromosome is transferred It remains as a recipient **b/c part of the F factor is never transferred to the recipient High frequency recombination |
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52. What is the prototype system for conjugation of gram-positive bacteria?
What do the donor cells (plasmid containing) do when stimulated? What stimulates them? What produces this stimuli? |
Enterococcus faecalis
Produce an adhesin **no sex pili A small, 7-residue peptide pheromone (hormone) Recipient cell |
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53. Once the recipient cell produces the hormone and it is sensed by the donor cell what happens?
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1. Donor cell produces adhesin
2. Clumping of donors and recipients 3. Transfer of plasmid DNA from donor to recipient by cell-to-cell contact |
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54. Why is conjugation important medically?
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Conjugation systems can account for the transfer of plasmid-mediated antibiotic resistance and even exotoxin production among gram-positive bacterial species
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55. What are three reasons for why plasmids and transposons are important?
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1. Major cause of bacterial antibiotic resistance
2. Some contribute to pathogenicity 3. Major components of recombinant DNA technology |
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56. How is the DNA in plasmids?
What are the size of cloning vectors? How are conjugative plasmids in size? Why? Are plasmids essential for bacterial growth under most conditions? |
Covalently closed, double-stranded circular DNA
Cloning vectors are fairly small Conjugative plasmids are larger B/c conjugation requires 20 or more genes No |
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57. How do plasmids replicate?
Due to this what are they called and why? What does the copy number of plasmids refer to? |
Replicate separately from the host chromosome
Replicons b/c they partition efficiently into both daughter cells at the time of bacterial cell division Refers to plasmids that have not integrated into the chromosome and are replicating autonomously |
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58. What are episomes?
In plasmid nomenclature, what does each part of the standardized name represent? Example: pBR322 |
Plasmids that can integrate into the chromosome and replicated as part of the chromosome
p - plasmid BR - code for lab where plasmid was isolated/constructed 322 - lab # to pinpoint particular plasmid |
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59. What are R plasmids or R factors?
What are many of the resistant determinants parts of? |
Plasmids that carry determinants (genes) for antibiotic resistance
**often they carry resistance determinants to several different antibiotics Transposons |
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60. How do plasmids (or transposons) that carry determinant for antibiotic resistance differ from chromosomal antibiotic resistance?
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Plasmid introduces a whole new gene that determines the resistance
Chromosomal antibiotic resistance is caused by mutation of an existing gene Chromosomal resistance usually results from alteration of the target of the antibiotic Plasmids cause resistance in a variety of ways, often by inactivating the antibiotic **For most gram pos. and neg. species plasmids are the main source of clinically important antibiotic resistance |
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61. What is the antibiotic target site for penicillins and cephalosporins?
What is the mechanism of plasmid resistance? What is the plasmid product? |
Cell wall
Enzymatic hydrolysis Beta-lactamase |
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62. What is the antibiotic target site for erythromycin and clindamycin?
What is the mechanism of plasmid resistance? What is the plasmid product? |
Ribosome (50S)
Modification of 23S RNA Methylase |
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63. What is the antibiotic target site for tetracycline?
What is the mechanism of plasmid resistance? What is the plasmid product? |
Ribosome (30S)
Pumps antibiotic out Inducible membrane proteins |
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64. What is the antibiotic target site for sulfonamide?
What is the mechanism of plasmid resistance? What is the plasmid product? |
Inhibitions of dihydropteroate synthease
Alternative (resistant) enzyme Sulfonamide-resistant dihydropteroate synthetase |
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65. What is the antibiotic target site for trimethorpim?
What is the mechanism of plasmid resistance? What is the plasmid product? |
Inhibition of dihydrofolate reductase
Alternative (resistant) enzyme Trimethoprim-resistant dihydrofolate reductase |
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66. What is the antibiotic target site for streptomycin spectinomycin?
What is the mechanism of plasmid resistance? What is the plasmid product? |
Ribosome
Block transport into cell Enzyme for modifying antibiotic |
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67. What is the antibiotic target site for kanamycin, gentamicin, tobramycin, and amikacin?
What is the mechanism of plasmid resistance? What is the plasmid product? |
Ribosome
Interference w/ transport into cell Enzyme for modifying antibiotic |
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68. What is the antibiotic target site for vancomycin?
What is the mechanism of plasmid resistance? What is the plasmid product? |
Cell wall
D-Ala-D-Lac in peptide side chain New enzyme |
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69. What is an example of some plasmids contributing to bacterial pathogenicity?
How do conjugative plasmids transfer? What can conjugative plasmids do to non-conjugative plasmids? Is plasmid transfer/replication species specific? |
Major virulence factors of B. anthracis are encoded on two large plasmids
Mediate their own transfer from one bacterium to another via conjugation Can mobilize them to transfer w/ them during conjugation Some replicate in a very limited range of species while many can cross species barriers and take their resistance w/ them |
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70. What is incompatibility?
How are closely related plasmids? Why? |
Ability of two plasmids to co-exist stably in the same bacterial cell
Incompatible B/c they compete for the same replication machinery |
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71. What is the most sensitive, quick way to screen for plasmids?
What are transposons? |
Extract them from bacteria and analyze them by agarose gel electrophoresis
**fractionation is by size Defined pieces of DNA that can move (transpose) as discrete units from one site in a DNA replicon to another site in the same replicon or in another replicon |
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72. Are transposons replicons?
What are the replicons then? What do many transposons carry? |
No they are not replicons themselves
Replicon = bacterial chromosome, bacteriophage DNA, plasmid Drug-resistant determinants |
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73. What are insertion sequences or IS elements?
What do they code for? When are IS elements most easily detected? |
The smallest transposons
Code for their own transpositions (for transposases) but have no readily observable phenotype of their own When they insert in a gene, inactivating and yielding a mutant that does have a phenotype |
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74. What is the structure of a typical IS element?
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1. Genes for transposition only
2. Inverted repeats 3. Direct repeats at target |
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75. What is a composite or compound transposon?
What does a compound transposon have that an insertion sequence does not have? What is an example of a composite transposon? |
Two copies of an IS element that have teamed up
Does have an overt phenotype Tn10 which has two copies of IS10 flanking a gene for tetracycline resistance |
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76. What is one way to make different composite transpososn without changing the IS elements?
How do compound or composite transposons tranpose? What does the spreading of vancomycin resistance in enterococcus result from? |
Place different pieces of DNA between the IS elements
As an unit **sometimes one of the IS elements will transpose by itself Multi-gene cluster transposon that is usually on a plasmid **vancomycin resistance is plasmid determined |
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77. What does the Tn916 determine?
What type of transposon is this? What does it do? |
Determines resistance to tetracycline
**found on E. faecalis Conjugative transposon Induces bacteria to conjugate w/o any plasmid **"plasmid-free" transfer of drug-resistance determinants from one E. faecalis to another **Tn916 can also induce conjugation between species |
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78. What does Tn916 mediate conjugation between?
Since conjugative transposons are widely distributed what are they referred to as? |
Mediates its own conjugative transfer between a wide range of species including gram-negative and gram-positive species
Integrative and conjugative elements (ICEs) |
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79. What is a summary of transposons properties?
Five properties... |
1. Transpose (move)
2. Insertion is stable (1 in 10^8/generation) 3. Can carry resistance genes or genes for pathogenicity 4. Some are conjugative 5. NOT replicons |
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80. In summary what are the characteristics of transposition?
Five things... |
1. Site-specific recombination
(specific ends for transposon) 2. RecA independent 3. Homology not required 4. Insertion can disrupt gene 5. Insertion can be on a plasmid or on a chromosome |
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81. How is the methicillin resistance in MRSA caused?
What is MRSA generally resistant to several antibiotics? How are the mobile elements of MRSA? |
Caused by the appearance on the chromosome of a new gene (mecA) for a penicillin-binding protein
B/c the mecA gene is part of a novel type of mobile genetic element Big and generally contain IS elements, transposons and integrated plasmids |
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82. What are Staphylococcal cassette chromosomes (SCCmec)?
What are most types of SCCmec associated with? What is the SCCmec type IV associated with? |
Large MRSA genetic elements
Hospital acquired (nosocomial) MRSA infections Community-acquired MRSA |
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83. What type of recombination is transposition?
How is it different from homologous recombination? (two ways) Where is the site of recombination specific for in transposition? What is another example of site-specific recombination? |
Site-specific recombination
1. Does not require extensive homology between donor & recipient 2. Does not require RecA protein Specific for the ends of transposons Lysogeny |
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84. In a nut shell how does gene expression come about?
Where does the regulation of gene expression in bacteria occur? |
1. DNA is transcribed by RNA polymerase to give RNA
2. RNA is translated on ribosomes to give proteins Occurs at the level of transcription |
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85. What does bacterial RNA polymerase consist of?
What is the fifth protein subunit called? What is the holo enzyme? What does the holo enzyme do? |
Core of four protein subunits α₂ββ'
Sigma (σ) which binds to the core giving the holo enzyme α₂ββ'σ Holo enzyme binds to a DNA sequence called the promoter and starts to transcribe the DNA |
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86. Where is the promoter located
In what direction does transcription proceed? How does this structure of bacterial RNA polymerase compare to eukaryotic RNA polymerase? What is the target of the rifamycin series of antibiotics? |
Located upstream from the transcription start point
Proceeds in the direction away from the promoter Structure is significantly different **good indicator to search for antibiotics Bacterial RNA polymerase is the target |
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87. What confers promoter recognition to the holo enzyme?
When the holo enzyme binds to the promoter region what is formed? How is an open complex then formed? Once transcription starts, what happens to the sigma factor? |
Sigma factor
Closed complex Part of the DNA double helix unwinds to form an open complex It falls off and the core enzyme continues transcription |
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88. In E. coli and B. subtilis where are the sequences that the sigma factors recognize?
What conforms closely to this promoter consensus sequence? What conforms less closely to the consensus? |
Approximately 35 bases and 10 bases upstream of the transcription start site
Strong promoters that direct high-level transcription Weak promoters giving only low level transcription |
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89. What terminates transcription?
In general when do these structures only form? What are the two type of termination signals? |
Transcription termination signal in the recently formed RNA
Only form when the RNA is not being translated into protein **translation often prevent transcription termination 1. Rho-dependent *need a protein Rho for termination to take place 2. Rho-independent |
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90. What are Rho-independent termination signals?
How are some genes expressed in bacteria? |
RNA hairpins followed by a run of U's
Constitutively **they are on all the time **but the expression of many genes is regulated |
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91. Is E. coli lac+?
What does this mean? Why is it lac+? |
Yes
It can use lactose as a carbon source B/c if the lac operon |
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92. What type of genes are lacZ, Y, and A?
Why? How are the three genes transcribed? Then what are the translated into? What do these proteins allow E. coli to do? |
Structural genes
B/c they code for protein products Transcribed into only polygenic (polycistronic) messenger RNA (mRNA) Translated on ribosomes into three proteins Protein products enable E. coli to use lactose and other β-galactosides as carbon source |
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93. What is the product of lacZ?
What does it catalyze? What is the lacY product and what does it catalyze? What is the lacA product? |
β-galactosidase
Hydrolysis of β-galactosides to more readily metabolized sugars Permease which catalyzes the uptake of β-galactoside Transacetylase **role is unclear |
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94. What does it mean to be Lac-?
What is an operon? What is part of the Lac operon? What is not part of the Lac operon? |
Make no active β-galactosdase or no active permease so cannot metabolize β-galactosides
Group of adjacent genes whose transcription is regulated from a single operator region Lac operon - Z, Y, & A (also O & P) lacI gene is not part of operon **lacI gene works equally when when it is moved to a different part of the chromosome **lacI gene has own promoter |
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95. What is the lacI gene?
What is the repressor or regulator? When no β-galactoside is present what does the repressor do? |
Structural gene for the repressor (regulator)
Allosteric protein which has dual affinity for β-galactosides and for the operator (lacO) Binds to the operator and keeps expression of the lac operon "off" |
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96. What is the lacO?
When is there no transcription (off)? Where is there transcription (on)? What does the inducer do when present? Due to the inducer what term is used to describe the lactose operon? |
The operator or "on-off" switch for transcription of the operon
Repressor protein is bound to operator (off) Inducer (β-galactoside) is present (on) It binds to the repressor altering its conformation so that the repressor loses affinity for the operator Inducible System |
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97. Why is the Lac repressor (lacI) a trans-acting factor?
Why is the Lac operator (lacO) a cis element? What is the P region on the Lac operon? |
B/c it diffuses through the cytoplasm and acts on lacO which does not need to be near the lacI gene on the chromosome
B/c it only controls genes that immediately adjacent to it on the chromosome Promoter where the RNA polymerase binds |
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98. What happens when the lacI gene is mutated so that repressor function is lost?
What are such mutant known as? |
No repression so genes of lac operon are expressed all the time
**expressed constitutively LacI- |
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99. What type of control is the lac repressor-operator system under?
What does this mean? |
Negative control
Means that the operon is under the control of a repressor |
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100. What controls to trp operon?
What type of factor is the Trp repressor? What does deletion of the trpR gene result in? When does the Trp repressor repress the trp operon? |
Controlled by the Trp repressor **coded for by trpR
Trans-acting factor Constitutive expression of the trp operon Only represses the trp operon in the presence of tryptophan **only want to make tryptophan when there is none there |
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101. When E. coli is grown with glucose what happens to the lac operon?
What mechanism does this? What does this mechanism involve? (two things) |
Expression of the lac operon is shut off
**even if β-galactoside is present Carabolite repression 1. cAMP *cyclic adenosine monophosphate 2. CRP - regulator protein *catabolite repressor protein |
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102. How does the intracellular concentration of cAMP vary with the glucose concentration?
What happens when cAMP concentration is high? |
If glucose is low, cAMP is high
Binds to and activates CRP |
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103. What type of regulator of the lac operon is the cAMP-CRP?
Where does the cAMP-CRP bind? What is binding of the cAMP-CRP near the promoter necessary for? |
Positive regulator
Near the promoter Efficienty RNA polymerase binding to the promotor **greatly increases transcription |
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104. In the presence of glucose what happens to the lac operon?
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1. cAMP concentration falls
2. cAMP-CRP concentration falls 3. Transcription of lac operon is greatly reduced |
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105. What are the two controls of the lac operon?
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1. Only efficiently expressed when a β-galactoside is present
**so that lacI doesn't bind 2. Only efficient when there is no glucose **so cAMP-CRP does bind |
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106. How can you tell positive control from negative control?
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Delete the regulatory gene
Example: delete lacI and you get constitutive expression of the lac operon |
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107. How is catabolite repression an example of a global regulatory system (or global regulon)?
What is another example of global regulation? |
So long as E. coli has a good C source it doesn't waste energy in making enzymes to utilize poor C sources even when they are present
**Organism effects major changes in metabolism as a response to environmental changes The repressor controlling the SOS response to DNA damage in E. coli |
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108. What mediates the SOS repsonse?
(two things) What happens in the SOS response? (four steps) |
LexA repressor and recA protein
1. RecA is activated by DNA damage 2. RecA causes proteolysis of the LexA protein 3. LexA repressor activity is inactivated 4. Several genes are turned on (de-repressed) including various genes for DNA repair |
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109. What has the two-component sensor-effect regulation system been found to be a response to?
Why type of regulation system is it? What do two-component systems regulate the expression of? What two protein components do these systems have in common? Why are these systems targets for the development of new antibiotics? |
Many different signals from a bacteria's environment
Global regulation system Regulate the expression of virulence genes in many pathogens 1. Histidine kinase (sensor) 2. Response regulator (effector) Two component systems have not been found in higher eukaryotes |
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110. In response to some environmental signal what does the sensor or histidine kinase do?
(two things) What is the second protein commonly? |
1. Phosphorylates itself
2. Transfers phosphate to aspartyl residue on second protein activating it A regulator of transcription |
